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The present invention relates generally to methods and apparatus for treating oil/water emulsions, and more particularly to methods and apparatus for coalescing and separating water from oil in an elongate, horizontal separation vessel.
Oil wells typically produce a mixture of oil, gas, and water, typically salt water or brine. The brine might be mechanically mixed with the oil to form what is commonly called an emulsion. The emulsion generally includes small droplets of brine that are suspended in oil. Even though the brine is heavier than oil, the small droplets might remain in suspension for a considerable period of time unless steps are taken to separate the brine from the oil.
It is desirable to separate the oil from the water and gas at the wellhead to facilitate handling of the constituents. The brine may be pumped back into the field and the gas collected or flamed-off, for example, while the oil is transported for further processing. The device used for this is commonly known as a treater.
One general method that has been used to separate brine from oil is to coalesce brine droplets so that they obtain sufficient size to separate from the oil by gravity. Treaters incorporating mechanical, electrostatic, and mechanical-electrostatic techniques have been used to coalesce brine for its separation from emulsions. The emulsion is typically heated, which lowers the viscosity and facilitates separation of the gas. The heated emulsion is then forced through a separation device. Some separation devices have included horizontal louvers directing the emulsion flow to electrostatic grids or packing. One type of packing is essentially a panel of xe2x80x9choneycombxe2x80x9d cells or tubes sloping downward from the inlet end of the cells to the outlet end. Brine coalesces from the emulsion traveling through the tubes, forming droplets large enough to separate from the oil by gravity. Unfortunately, sludge can build up on the horizontal surfaces. The louvers and packing also sit within the oil portion of the treater, and an asphalt-like pad can develop at the oil-water interface. This pad interferes with the separation process, and consumes treater volume. Eventually, the treater may have to be brought off-line for cleaning.
Another approach uses externally controllable vertical louvers to control the flow of emulsion through the treater and to promote de-emulsification by creating vortices and laminar streams of water droplets flowing off the trailing edges of the louvers. Unlike other techniques that seek to avoid laminar flow, the vertical design of these louvers causes a fine sheeting action that provides laminar flow pathways for water to transverse the oil portion into the water portion of the treater. Coalescing elements, such as packing and/or electrostatic grids, are typically included to enhance the de-watering process.
It is desirable to provide simpler, more compact emulsion treaters that avoid sludge formation and re-emulsification. It is further desirable to provide flow control to adapt the de-watering process according to the properties of the incoming crude oil and/or selected water content.